The authors investigated the magnetic properties of Fe-doped zirconia, ZrO2:Fe, grown by atomic layer deposition, for different concentrations of Fe dopant, a substitutional impurity to Zr. Their growth recipe allows the deposition of films in which the percentage of Fe, x, ranges from diluted (x  ∼ 1–2 at. %) up to high (x ∼ 25 at. %) concentrations. By x-ray magnetic circular dichroism, the authors carefully analyzed the magnetic moments of these dilute magnetic oxides at low temperature (T = 5 K), determining the best dopant range maximizing the magnetic signal. In particular, the authors found that the magnetic signal decreases as the Fe concentration increases. By comparison with ab initio simulations, the authors enlighten the microscopic mechanisms responsible for this peculiar behavior.